CYB-375 The date is no longer returned in the /gallery/index feed

 * adding the 3 date fields that are taken from the Canvas API return values
   for each asset type to the selected values returned

https://jira.ets.berkeley.edu/jira/browse/CYB-375
Merge branch 'add_date_to_gallery_index_feed' of https://github.com/coyote/datacultures into add_date_to_gallery_index_feed